The study will examine semen and serum biomarkers of male reproductive function in partners of pregnant women recruited from 4 US centers (LA,Minneapolis, Columbia, New York). This study will constitute the US component of an international study which started in 1996 in 4 centers in Europe. The Harbor-UCLA Medical Center will recruit 300 male partners of pregnant women in 12 to 18 months. The study should provide unbiased estimates of variability among cities in the US and provide baseline levels of male semen data and biomarkers of male reproductive function for future studies.